usb: Remove usb_dev_init() from ehci-ppc4xx.c

Calling usb_dev_init() from within the EHCI host driver is wrong.
The EHCI host driver should have no dependency/interconnection to the
USB device driver.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Remy Bohmer <linux@bohmer.net>